Two overarching themes of the biomedical research of this Superfund Program addressed in this project[unreadable] relate to a) the metabolism of arsenic (As) and b) As-induced oxidative stress. There is significant variability[unreadable] in progression from As exposure to clinical manifestations of disease. Several studies have led to the[unreadable] hypothesis that nutritional status may account for a substantial portion of this variability. Inorganic As is[unreadable] methylated via one-carbon metabolism, a biochemical pathway that is dependent on folate for recruitment of[unreadable] one-carbon groups. We wish to expand our studies, which have begun to characterize the impact of[unreadable] nutritional regulation of one-carbon metabolism on the inter-individual variability in As methylation.[unreadable] Glutathione (GSH), a key component of the primary antioxidant defense mechanism, and the electron donor[unreadable] for As reduction, is synthesized from homocysteine, and this synthesis is regulated by intermediates of onecarbon[unreadable] metabolism. A great deal of basic research, including salient work from members of our group,[unreadable] points to the growing belief that As depletes glutathione (GSH) and induces oxidative stress. However, the[unreadable] relationship between As exposure and oxidative stress has not been rigorously examined in human[unreadable] populations.[unreadable] The first specific aim of this proposal will utilize the repository of biological samples established by the[unreadable] Cohort Study (Project #2) to conduct a nested case-control study to identify modifiable risk factors (e.g.[unreadable] oxidative stress and/or hyperhomocysteinemia) related to increased susceptibility to As-induced skin lesions.[unreadable] The remaining specific aims will take advantage of the expansion of our study area (and installation of Asfree[unreadable] tube wells) in Projects #3 and #7 to recruit 375 new adults who are currently exposed to As. In Specific[unreadable] Aim 2, we will address a fundamental question: To what extent do urinary As metabolites reflect As[unreadable] metabolites in the circulation? In Specific Aim 3, we will conduct a cross-sectional study to test the[unreadable] hypotheses that higher concentrations of s-adenosylhomocysteine (SAH) and lower concentrations of GSH[unreadable] are associated with reduced As methylation. In Specific Aim 4, we propose to examine dose-response[unreadable] relationships between As exposure and oxidative stress. Finally, we will test the hypothesis that reduction of[unreadable] As exposure alleviates oxidative stress. The proposed studies have the potential to a) substantiate that As[unreadable] induces oxidative stress and depletes GSH in a human population, b) link As-induced oxidative stress and/or[unreadable] nutritional status to an arsenic-related clinical outcome, and c) expand our understanding of the mechanisms[unreadable] underlying these processes. Such findings would have significant implications for the identification of[unreadable] potential targeted interventions for preventing As-toxicity.